Reference is made to a U.S. Pat. Nos. 4,796,179, 4,860,203 and 4,831,580, a Japanese Patent Laid-open Publication JP-A-1-237726 and R. Rock-Evance and K. Hales, "Reverse Engineering: Markets, Methods and Tools", Vol. 1, Ovum Ltd., 1990, pp. 3 to 33. These background arts describe software reuse or reengineering between external and internal designs, i.e., between upper and lower level specifications.